textproduct: Rapid City

KEY MESSAGES

- Near average temperatures through the weekend with highs mainly in the 70s.

- Another lobe of tropical moisture expected early next week, supporting more chances for rain Sunday and Monday, starting especially Sunday evening.

- Slightly cooler next week.

UPDATE

Issued at 1028 PM MDT Fri Sep 25 2026

Based on current trends in sfc obs and consensus between NBM and HRRR guidance, somewhat generously added patchy fog to the forecast across the South Dakota plains north and east of Rapid City extending out toward Winner and the Missouri River corridor. Overall coverage may be a bit less than last night. Areas of low stratus clouds are also expected and are already observed on satellite and sfc stations in some of the same areas. Confidence on patchy fog and/or low stratus reaching as far west as the Rapid City area is very low at this time, with best potential definitely north/east.

DISCUSSION

(This Afternoon Through Thursday) Issued at 1144 AM MDT Fri Sep 25 2026

Upper trough will remain in place through early next week over the western CONUS, supporting mainly WSW flow aloft. Pattern change expected toward next weekend as a strong NE Pac upper trough dives into the Pac NW and supports a couple stronger upper troughs and associated sfc low's across southern Canada and the northern CONUS. Lingering monsoon wave will phase with a stronger upper trough moving across southern Canada today into Sat. Enough diurnal instability will be in place to support isolated to scattered showers/storms in the SW FA. However, the better chances for rain will be to the east of the FA where deeper moisture is in place. Associated cool front will move through Sat with breezy NW winds developing over western SD for a bit. Drier air will move into the region, supporting dry weather through most of Sunday before the next upper trough and batch of tropical moisture advects into the region. Upper trough will drop into the SW CONUS Sunday and direct tropical moisture NE across the Rockies. The path of this moisture and the location of best forcing is still not settled in forecast models and will hinge on the upper closed low's track, which are difficult to predict for forecast models. Hence, rain chances are likely to change in the next few model cycles. The best window for rain will be Sunday night into Monday, with things drying out after. Slightly cooler, but seasonal the rest of the week. Models are still indicating a stronger cold front next weekend, which could bring a widespread frost as the upper trough over the NE Pac shifts east and forces cold air south out of Canada. However, the degree of CAA with this system varies substantially among the various forecast models and ensembles.

AVIATION

(For the 06Z TAFS Through 06Z Saturday Night) Issued At 945 PM MDT Fri Sep 25 2026

VFR conditions are expected for northeast Wyoming and far western South Dakota through the TAF period. Low clouds will stick around across the south-central South Dakota plains, expanding west into parts of northwest and southwest South Dakota during the overnight hours tonight. Patchy fog and low cigs may lead to IFR/LIFR conditions in this same region through Saturday morning. At this time, the fog and low stratus are not expected to reach KRAP, but once again it may be close. Conditions will improve west to east, with most areas returning to VFR by the end of the TAF period. Winds will shift to northwest Saturday morning.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.